This site's footer says it directly: if you have diabetes or prediabetes, or take any medication including insulin or metformin, consult your physician before use.
Three groups: people with diabetes, people with prediabetes, and anyone on any medication. That last group is wider than blood-sugar drugs alone.
The instruction is to consult first, which leaves the decision with you and your physician. The FAQ's "Who should avoid GlucoPril?" answer repeats it.